Conventionally, the shift range switch device, or the gear shifter, performs the reference value check by performing an “abutment learning” in a technical phrase in the art. For example, a patent document, JP 2013-59162 A (patent document 1) in the following discloses such a learning.
The gear shifter includes a drive object driven by a motor torque from a direct current motor to shift from one position to the other, for enabling a gear shifting of an automatic transmission, a stopper regulating a move range of the drive object on one end of the move range, a position detector outputting a position signal indicative of a position of a rotor of the motor, and a controller controlling an operation of the motor based on the position signal.
In the gear shifter of the patent document 1, the drive object is provided as a one-body combination of a detent plate and a control rod together with other parts, and the stopper is a detent spring. The position detector is an encoder included in an electric actuator.
Further, a microcomputer in an Steer By Wire-Electronic Control Unit (SBW-ECU) serving as the controller uses the position signal from the encoder as a signal indicative of a shift range, or a gear position, for determining to which the shift range, or the gear position, the gear shifter is currently set.
Then, upon receiving a shift range switch instruction, the controller controls the electric actuator based on the position signal, and shifts the drive object so that the instructed shift range is set.
In such control scheme of the gear shifter, the position signal from the encoder is a count value with reference to a certain reference value that is set after a start-up of an Electronic Control Unit (ECU). Therefore, once a reset of such reference value is performed, the reference value must be set again.
For example, in case a memory of the reference value is lost during a sudden power interruption during a travel of a vehicle, the reference value must be set again during an initialization of the shift range switch device.
The setting of the reference value is performed based on an abutment learning. That is, in the abutment learning, the drive object is abutted to a certain stopper, and the position signal indicative of such a position of the drive object is set and used as the reference value.
However, the abutment of the drive object to the stopper causes a warpage on both of the drive object and the stopper. Further, the amount of warpage may change depending on the temperature or the like, thereby possibly causing a variation of the reference value.